It is reported that some people see flicker or experience eye strain or headaches when working with LED backlit monitors. This would be caused by pulse width modulation where the backlighting is switched on and off rapidly at varying on and off times to change the brightness. If this frequency of on and off switching, the pulse width modulation frequency, is below 500Hz or even 1kHz, these problems are reported by some people and not by others. Although the brightness of most CCFL backlit monitors is also changed using pulse width modulation, this is less of an issue because the CCFL tubes don't turn off completely during the off cycle, because they have some after glow, reducing the on/off contrast.

Here's my question: have you experienced any of these issues - flicker, eye strain or headaches - when using an LED backlit monitor and if so, which monitor did you use and do you know by any chance the pulse width modulation frequency?

That answer will depend greatly on the specific monitor and individual person. Each person's brain will be operating on slightly different frequencies and vary through the day. Mine is rather quick and I see the flicker of most LED bulbs quite easily such as xmas lights. It drives me crazy but my wife can't see a thing. I can see it even on FL backlights but it doesn't cause me any issue, and I have never had an issue from LED backlit screen on my laptops. For example I have used this Dell 24" for years and it's a cycle or two less than my Dell 27" - both FL. You can see it quite easily on video, even though both are 'running' at 60Hz in the OS and rated for 60Hz by Dell equally.

A non-issue, Andrew? Really? Many people have issues when the LED pulse width modulation frequency is below 1500Hz or so and many LED monitors operate well below that. If by any chance you might be interested in educating yourself, I'll be happy to provide you with links to articles on this issue.

There you go Frans, your answer and maybe one you'll actually accept. One user here who has an issue, all those links you know of, those of us that say no issue. What is the next set of windmills to chase?

You finish that piece from the CIE that talks about how calibrating to D50 doesn't always (often not) work?

Andrew, You really want to compare an issue that can cause epilepsy, migraine, retinal desease, urticaria, eye strain, nausea, etc, etc. with tilting at windmills and deride me for having an interest in this issue? I happen to be considering buying the NEC P232W and it was brought to my attention on this website that it has a very low PWM frequency and might cause issues for many people, so I'm trying to learn more about it. Is that OK with you?

And since you brought up the issue of "that piece" again, let me refresh your memory: I said at the time that I would not respond to your personal attacks and nothing has changes since then. Have a nice day.

You really want to compare an issue that can cause epilepsy, migraine, retinal desease, urticaria, eye strain, nausea, etc, etc. tilting at windmills? And who are you to deride me for having an interest in this issue?

Point me to the source of epilepsy, migraine, retinal desease, urticaria, eye strain, nausea caused by LCD displays please. The last two identical posts you started here and on PhotoNet resulted in your identical behavior, asking questions and dismissing anything but the answers you predicted what you wanted to hear. I suspected this third post was going to be yet another similar tactic on your part, I don't as yet think I'm wrong.

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I happen to be considering buying the NEC P232W and it was brought to my attention on this website that it has a very low PWM frequency and might cause issues for many people, so I'm trying to learn more about it. Is that OK with you?

Fine, buy the unit, and if you have an epileptic seizure, send it back or better, get a demo at a good VAR before you put down your money. If 3 out of 30,000 people here reported that yes, they had a migraine by viewing an LCD backlit display, you'd do what with that info and that would change how you purchase and return it how? And you didn't specifically ask about this NEC in your original post, you asked about LCD's in general (that's telling). Hence the comment about windmills. This is much like your flat earth theories about Solux CCT values (which as promised, you failed to report back about, again telling). You are now apparently after someone writing something agreeing with reports that some people see flicker or experience eye strain or headaches when working with LED backlit monitors. and like your Solux quest, you now aiming at NEC based on your last post. Just tell us what answer you want to hear and someone will hopefully provide it so you will go your own way.

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And since you brought up the issue of "that piece" again, I apparently need to refresh your selective memory: I told you then that I would not respond to your ad hominem attacks and nothing has changed.

I wasn't the only one that asked you to comment about the article that blasted holes in your theories about display calibration. That you haven’t commented to anyone and would rather refrain from admitting the article shows your severe misunderstanding of the issue, it is no wonder you would blame your lack of a response on me. The truth is, you don't have the honesty to read what an actual color scientist wrote that points out the flaws in your understanding of color and dismisses the article on the subject YOU yourself posted for comment on PhotoNet. Again, telling.

What's your agenda Frans? You started a post, filled with a lot of nonsense about Solux CCT values. You started another concerning differing products reporting differing values of CCT from the same xyY values and in both cases, the correct replies you got, you didn't accept. You did this on two sites and got the same answers. You are back now apparently looking for problems with some, all or a specific NEC display of which whatever answer you get, it will not be accepted. What stops you from purchasing this NEC, testing it and either keeping it or returning it if you suffer from your head exploding? There's a Linkedin forum for NEC users, why not ask there?

And since you brought up the issue of "that piece" again, let me refresh your memory: I said at the time that I would not respond to your personal attacks and nothing has changes since then.

There's a significant difference between not being able to respond to an article and not willing to respond. You are unable to respond as the author of the piece submitted to the CIE has far more credibility, an understanding of the subject, and a scientific approach and the article can and does withstand peer review. Your's does not. You are unable to respond because the article uses science and facts to poke holes in your article that used neither.

"get a demo at a good VAR before you put down your money": OK, Andrew, tell me where in the greater Portland, OR area I can find a VAR that can demo me the various high-end NEC monitors, or any high-end monitors for that matter.

"And you didn't specifically ask about this NEC in your original post, you asked about LCD's in general (that's telling). ": I DID ask specifically about the NEC P232W in a previous post, but since I didn't get much reaction, I widened the question to all LED monitors in the hope of getting some useful feedback, if that's OK with you; by the way, YOUR responses haven't been particularly helpful, have they?

"What's your agenda Frans?: My "agenda" is to learn about LED backlit monitors in general and, if there is anybody using the P232W, about that monitor in particular. What's your agenda, Andrew? Oh, never mind. It's pretty obvious.

"There's a significant difference between not being able to respond to an article and not willing to respond.": I'll only repeat this one more time - I told you then and I tell you now that I won't respond to that series of personal attacks. Go read what you wrote then and tell me if YOU would respond if somebody used that kind of language. Have a nice day.

"There's a significant difference between not being able to respond to an article and not willing to respond.": I'll only repeat this one more time - I told you then and I tell you now that I won't respond to that series of personal attacks.

Sorry if the concept of peer review, a process that pokes holes in your concepts seems like an attack. Keep in mind you brought up the subject! This is the result of your original post on PhotoNet you started introducing readers to your new article on the Solux site that's incorrect in a number of areas. The CIE article simply points out the folly of your assumptions. The article I reference has zero personal attacks. It does dismiss your piece. You know it, I know it. You can't defend it. End of story.

The quest to find how, if, and when some backlit LCD will produce migraines,epilepsy etc is, as told to you on both forums, based on the display and or course the end user. No matter what anyone tells you, the quest only fulfills itself when you purchase or demo said display and suffer migraines,epilepsy etc. The rest is just a quest filled with verbal diarrhea and serves no purpose. Find a VAR, look at whatever display you think you'll purchase and if it produces a migraines,epilepsy etc, you probably shouldn't buy it. How's that for sound advise?

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by the way, YOUR responses haven't been particularly helpful, have they?

Only in again, you can never accept an answer that you don't want to hear. I told you I have NO issues with the LED backlit displays I have. Maybe if I told you I suffered migraines,epilepsy etc, you'd have enjoyed the post a tad more.

"Pro Photo Supply...good company." Oh, that company! You mean the one that doesn't sell NEC? You mean the one that sold me a Hurricane blower that blew tiny rubber particles onto my DSLR's sensor that wouldn't come off, so it had to be returned to Nikon for repairs and then let Nikon pay for it? The company that kept selling the Hurricane blower while they were aware of what it did? You really mean that company? Yeah, I have a lot of confidence in them!

Any comments on the articles I referred to or are those people just as uninformed as I am?

Yes, some people, a tiny group may suffer migraines,epilepsy etc, are you in that category? IF so, then don't you think you'd want to:1. Avoid any or all LED backlit displays? 2. Test any you might buy? 3. Dismiss anything anyone else reports because they probably do not suffer these effects which your articles point out are affecting a tiny amount of users? Or like your post on PhotoNet, it's the grassy knoll conspiracy issues of NEC, producing on purpose a display that would produce these effects, then forcing those people to spend more on a display? You wrote:

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I'm interested in this issue because I plan to buy an LED backlit monitor, not because I have one already. I've asked NEC why one monitor has a pulse width modulation frequency of 180Hz (anything below 500Hz or even 1kHz may cause issues for some people) and the other two have 8kHz and 20kHz. As en electrical engineer I believe it would be easy to increase the frequency of the 180Hz one to something well above 1kHz. I hate to think that NEC would use 180Hz for the lower cost, 23" monitor on purpose, so they could sell up if people have issues with it, but you never know. I'm waiting for NEC to respond; their chat and next higher level support people didn't even understand the term pulse width modulation frequency, as far as I could tell, and my questions have been bumped up to engineering in Chicago and/or Japan.

You are waiting on NEC, much like you are waiting on Solux which apparently smartly ignores you. And IF NEC told you there's no such issue, as a sufferer of migraines,epilepsy etc, you'd buy the display without the ability to take it back? Again, what's really your quest here Frans? There is no issue. The display is either going to cause you migraines,epilepsy etc and you should be smart enough before you buy, or it isn't. No matter how many people tell you what you've heard here (some have no issues, some see issues), what's the point? You yourself will have to sit down in front of whatever you buy and see if you suffer migraines,epilepsy etc. IF and WHEN that happens, we're all ears. Until then, what exactly do you want us to tell you?

"You are waiting on NEC, much like you are waiting on Solux which apparently smartly ignores you." It just so happens that SoLux has acknowledged that they have a problem. Stay tuned. And NEC apparently has a problem to formulate a response to my simple question in a timely manner: why is the PWM frequency of the P232W so low and are you planning to change it?

Yes, you are right: Eizo is high end, but I won't buy their products. And thank you so much for pointing out that I could buy on the internet with a solid return policy. Gee, I never even thought of B&H (where I buy most of my photography related items anyway). Should I refresh your memory and tell you again that I am trying to learn about LED backlit monitors before I jump?